Marian E. Stewart, an 80-year-old woman, was a patient in the intensive care unit at Community Hospital of the Valleys in Perris, California, when she became one of the patients later determined to have been murdered by registered nurse Robert Rubane Diaz. Although the supplied date is April 14, the California Supreme Court record places Stewart's fatal episode in the early morning of April 13, 1981.
She had already been hospitalized for several days and was seriously ill with respiratory failure associated with obstructive pulmonary disease and pneumonia, along with possible congestive heart failure. The day before her death, cardiac problems had caused her to stop breathing, but hospital personnel successfully revived her. Because she was also experiencing an irregular heartbeat, she was receiving lidocaine, a medication routinely used to control dangerous cardiac rhythm disturbances.
During the night shift, activity intensified in the ICU. Another patient, Kenneth Silvera, was also experiencing cardiac problems and was being treated with lidocaine. At one point Diaz went to another floor and told a nurse that an ICU patient was “going sour,” indicating that he expected an emergency. Stewart was aware of the activity surrounding Silvera and became frightened, telling staff that she feared she was going to die. While Nurse Cheville was speaking by telephone with Stewart's physician about her condition, Diaz told Cheville that Stewart had developed tachycardia, an abnormally rapid heartbeat, and that he intended to give her lidocaine. Approximately an hour and a half later, Stewart suddenly went into ventricular fibrillation, a chaotic electrical disturbance that prevents the heart from pumping effectively. Cardiac and respiratory arrest followed. Hospital personnel attempted to revive her, but the efforts failed, and she was pronounced dead at 6:15 a.m. Unlike many of the other patients whose deaths would later be associated with Diaz, witnesses did not see Stewart suffer the violent seizures that became a conspicuous feature of the wider investigation.
Her death eventually took on a far different meaning as investigators examined an extraordinary concentration of suspicious deaths at the Perris hospital. Records reviewed by Riverside County investigators showed that 24 patients had died there between March 8 and April 20, 1981, prompting scrutiny of the hospital's ICU. Autopsies and toxicological examinations began revealing unusually high quantities of lidocaine in patients who had died after sudden deterioration. Investigators also found that Diaz had attended patients displaying the distinctive combination of seizures, respiratory arrest and other alarming symptoms. A May 1 search of Diaz's home produced syringes, an empty lidocaine box and a vial containing lidocaine, evidence that was later introduced at his trial.
Stewart's case became particularly important because the medical evidence did not depend upon witnesses having seen her suffer seizures. Prosecution cardiology evidence showed that her heart rhythm strips contained broad QRS complexes and an unusual rhythm known as torsade de pointes. An expert testified that those findings were consistent with exposure to a large amount of a Class 1 antiarrhythmic drug such as lidocaine. Toxicologists analyzing Stewart's tissues concluded that she had received approximately 1,000 milligrams of lidocaine shortly before her death, far beyond what the prosecution maintained could be explained by her legitimate treatment. A prosecution pathologist ultimately attributed her death to lidocaine poisoning, with pulmonary hypertensive heart disease contributing. Defense experts disputed whether the tissue concentrations necessarily proved an overdose, but the trial court rejected that explanation, and the California Supreme Court later ruled that the evidence was sufficient to support the finding that Diaz murdered Stewart by injecting her with a massive dose of lidocaine.
The investigation expanded beyond Stewart's death as authorities connected Diaz to a succession of patients who suffered sudden seizures and cardiac or respiratory arrest while he was working. Diaz had begun working the night shift at Community Hospital of the Valleys on March 29, 1981. Over the following weeks, numerous patients experienced extraordinarily violent medical crises. After leaving the Perris hospital, he worked at San Gorgonio Pass Hospital in Banning, where another patient died under similar circumstances. Investigators came to believe that Diaz had been using his access to vulnerable intensive-care patients and their intravenous lines to administer massive quantities of lidocaine.
Diaz was arrested at his Apple Valley home on November 23, 1981, and charged in connection with the deaths of 12 hospital patients. Eleven of the charged killings were associated with Community Hospital of the Valleys in Perris, while another occurred at San Gorgonio Pass Memorial Hospital in Banning. The prosecution alleged that Diaz deliberately injected the patients with lethal quantities of lidocaine while occupying a position of trust as their nurse. Diaz denied committing the murders and ultimately waived his right to have a jury determine his guilt, leaving the case to Riverside County Superior Court Judge John Barnard. His trial began on October 31, 1983, and involved extensive testimony concerning toxicology, cardiology, hospital procedures, patient records and the concentrations of lidocaine recovered from victims' tissues.
On March 29, 1984, Judge Barnard convicted Diaz of all 12 counts of first-degree murder and found multiple-murder special circumstances true. Stewart's death was therefore formally included among the murders for which Diaz was convicted. On April 11, 1984, Barnard sentenced him to death, rejecting the defense request for life imprisonment without the possibility of parole. The court emphasized that Diaz had been entrusted with gravely ill patients who depended upon his professional skill and care, yet had instead used that position to kill them with drug overdoses.
Diaz continued to challenge his conviction and death sentence, but in 1992 the California Supreme Court affirmed the judgment. The court struck 11 duplicative multiple-murder special-circumstance findings while leaving the convictions and death sentence intact. He was never executed. Robert Rubane Diaz remained under a sentence of death until August 11, 2010, when he died of natural causes while still a condemned California prisoner. Marian Stewart's death, initially occurring in the setting of serious existing illness and an apparent catastrophic heart event, thus became one of the central murders in a case that exposed a pattern of deliberate lidocaine poisoning inside Southern California intensive-care units.
